code: def test_multi_agent_bad_policy_ids(self):
      self.assertRaisesRegex(
          KeyError,
          "Policy IDs must always be of type",
          lambda: (
              PPOConfig().multi_agent(
                  policies={1, "good_id"},
                  policy_mapping_fn=lambda agent_id, episode, worker, **kw: "good_id",
              )
          ),
      )
  
file_path: ray/rllib/utils/tests/test_check_multi_agent.py
imports: import unittest
  from ray.rllib.algorithms.ppo import PPOConfig
  from ray.rllib.policy.policy import PolicySpec
label_desc: Use image node_id 2 for calling the TestCheckMultiAgent obj's underlying member method code with example usage: obj.test_multi_agent_bad_policy_ids() without return types